This invention relates to a method for inhibiting crystallization of trimethylolethane from supersaturated aqueous solutions thereof and to the crystallization-inhibited solutions prepared in accordance with that method.
Most commercial customers for industrial chemicals prefer to handle bulk raw materials in liquid form. Liquids can be handled economically in bulk by pumping and metering, thus avoiding the manual labor associated with transporting and opening solid-containing containers and weighing solid charges.
Trimethylolethane is a water soluble, crystalline, polyhydric alcohol which finds widespread use in the chemical industry particularly in the manufacture of alkyd resins, drying oils and plasticizers. Trimethylolethane (TME), while a crystalline solid in pure form, is for the above reasons advantageously shipped in bulk for commercial usage as its aqueous solutions. Of course, the more concentrated solutions can be made, the more cost efficient shipping and handling can be. Aqueous solutions of TME as concentrated as 80% solids can be shipped as heated solutions in insulated tank trucks. Aqueous solutions of trimethylolethane at 50% solids can be shipped (as solutions) so long as the outdoor temperatures do not drop below 0.degree.-5.degree. C. Also, 80% by weight solutions are regularly shipped in insulated tank trucks and are stopped in heated tanks. However, crystallization usually begins at about 50.degree. C.
TME is highly soluble in water (140g/100g at 25.degree. C.) and its concentrated aqueous solutions readily become supersaturated as the temperature gradually becomes lower. The term "supersaturated solution" as used herein has the same meaning generally understood in the art, namely a homogeneous solution which contains more of a solute (an excess) than is normally possible at a given temperature. If the solute is normally a solid, a supersaturated solution cannot exist in the presence of a solid phase because the excess dissolved solid promptly comes out of solution as a precipitate and the resulting liquid phase is merely saturated.
The solubility profile of TME in water is such that any cooling of concentrated aqueous TME solutions can easily result in solution supersaturation. Subsequently any crystallization of TME from solution results in reversion of the solution to a saturated one in the presence of the solid phase. Indeed, supersaturated solutions of TME can "crystallize" into a solid crystalline mass. Cooling of concentrated aqueous TME solutions resulting in crystallization during shipment, in storage tanks and in pumping and metering equipment can result in a plant manager's nightmare. There is little that can be done with the resulting solid crystalline mass once it forms in shipping containers or processing equipment except to find some way to heat the "mass" to redissolve the TME, or mechanically to remove the crystallized material from the crystal-clogged equipment
It is therefore an object of this invention to provide a method for inhibiting crystallization of TME from supersaturated aqueous solutions of trimethylolethane.
It is a further object of this invention to provide crystallization-inhibited aqueous trimethylolethane solutions and a method for preparing those crystallization-inhibited solutions.
It is still a further object of this invention to identify materials useful as stabilizers (crystallization inhibitors) for aqueous trimethylolethane solutions, and to provide a liquid, pumpable grade of aqueous high solids trimethylolethane solution exhibiting resistance to unwanted, premature crystallization of trimethylolethane from supersaturated solution.